(1) Field of the Invention
This invention relates to a polyamide hollow and/or non-circular fiber and a process for making the same. More particularly, it relates to a polyamide hollow and/or non-circular fiber having enhanced degree of hollowness and/or degree of non-circularity (modification ratio), and to a process for making the same.
By the term "polyamide hollow and/or non-circular fiber" used herein, we mean a polyamide hollow-core fiber having a circular cross-section or a non-circular cross-section, or a polyamide solid (i.e., non-hollow) fiber having a non-circular cross-section.
(2) Description of the Related Art
Polyamide hollow fibers are generally characterized as exhibiting a lower apparent density, a lower rate of heat transfer, a reduced pilling and unique optical effects such as higher opacity, or sparkle. Polyamide non-circular fibers are generally characterized as exhibiting a lower rate of heat transfer, a higher covering power, a higher bulk and unique optical effects. Therefore, polyamide hollow and/or non-circular fibers are used for construction of floor coverings such as a carpet, and for fabrics having an attractive appearance.
Attempts have heretofore been made to make polyamide fibers having an enhanced non-circularity and/or hollowness. As such attempts, there can be mentioned a method of using a spinneret having a special configuration (Japanese Examined Patent Publication No. 36-20770, Japanese Examined Utility Model Application No. 58-12856, U.S. Pat. No. 3,508,390, and Japanese Unexamined Patent Publication No. 48-42134), and a method of using a polyamide having a high degree of polymerization, i.e., exhibiting a high melt viscosity (Japanese Examined Patent Publication No. H1-37486). The method of using a spinneret having a special configuration has a problem such that the number of orifices in a spinneret plate is restricted. It is quite difficult to make a non-circular fiber having desired characteristics. In the method of using a polyamide having a high degree of polymerization, the fiber-making becomes difficult with an increase of the melt viscosity, and the degree of non-circularity (modification ratio) and the degree of hollowness are restricted.
Proposals of incorporating a metal salt of a fatty acid in a polyamide have heretofore been made, but there is no technical idea of making polyamide fibers having an enhanced degree of non-circularity (modification ratio) and/or degree of hollowness in these proposals. For example, Japanese Examined Patent Publication No. 48-28975 teaches that a magnesium salt of a carboxylic acid has a function of minimizing the deposit of a polyamide on a spinneret and preventing the yarn breakage when melt spun. Japanese Unexamined Patent Publication No. 62-62911 teaches that yarn breakage at a high speed melt-spinning is prevented by adding a magnesium compound including a magnesium salt of a higher fatty acid. Japanese Unexamined Patent Publication No. 63-92717 teaches that incorporation of an isoindolinone pigment and a metal salt of stearic acid in a polyamide prevents the undesirable reaction between the isoindolinone pigment and the polyamide.